In microelectronic applications, polymers that demonstrate high temperature resistance, such as polyimides and polybenzoxazoles, are generally well known. Precursors of such polymers, can be made photoreactive with suitable additives. The precursors are converted to the desired polymer by known techniques such as exposure to high temperatures. The polymer precursors are used to prepare protective layers, insulating layers, and relief structures of highly heat-resistant polymers.
As the dimensions of photolithographic patterns on wafers continue to shrink below 0.15 microns, greater demands continue to be placed on lithographic equipment and materials. To meet this challenge, the semiconductor industry is changing from aluminum based alloys and silicon dioxide to copper metal and low dielectric constant (low-k) materials to manufacture chips. Copper is known to have as much as 40% decreased electrical resistance. Moreover, when using low-k materials there is a decrease in capacitance, which is critical to improving integrated circuit performance, especially for higher density memory chips. More and more, the metal substrate and inter-dielectric layer materials are changing from aluminum based alloys and silicon dioxide to copper metal and the new low-k dielectrics. Copper has lower electrical resistance, carries higher current densities, and has improved electromigration resistance compared to aluminum. Thus, copper interconnects allow decreasing transistor size and shorter connections that result in faster, more powerful devices.
Copper metallization provides a challenge to the semiconductor industry since copper can act as a catalyst and destabilize systems that are optimized for coating over aluminum. In addition, cuprous and cupric ions present on the copper surface can bind strongly with some polymers and reduce the ability to dissolve the polymers during certain wafer coating processes, which leaves undesired and detrimental residues behind. Further, without good adhesion of overlying structures to the Cu, non-adherent oxides can form resulting in device failure. With the increased use of copper metallization in semiconductor devices, it is important to develop photosensitive coating systems that are compatible with copper and copper processing.